1. Field of the Invention
The present invention relates to display devices of the type having character display functions wherein, for digital display, the digit place or decimal place is adjusted, and an input data overflow in a predetermined digital display region is detected.
2. Description of the Prior Art
In a display device, the disagreement between digit places or decimal points of a certain number of digits displayed in rows will require the operator to exert extra readout efforts or cause read error. (For explanatory simplicity, a character display device will essentially be considered hereinafter.)
Presently, digit place designation, decimal place designation, and overflow indication are displayed, for example, on an electronic calculator. The display available on an electronic calculator is only of digits or specific symbols, and such display appears in a predetermined position. Further, on an electronic calculator, the number of digits which can be displayed is limited. Whereas, in a character display device, a variety of digital displays can occur anywhere on the screen. This has made it difficult to designate a digit place or a decimal place and to detect overflow in a character display device. For more information on the prior art display, the outline of a character display device will be described below.
FIG. 1 is a block diagram showing an example of a character display device comprising an interface control part 1, a display control part 2, a cathode-ray tube (CRT) 3, and a keyboard 4. The interface control part 1 comprises a line interface part 8 and a message control part 9. The display control part 2 comprises a CRT controller 10, a refresh memory 11, a video circuit 12, and a timing circuit 13 for supplying a timing signal. The interface control part 1 controls data from or to a computer 6 by way of a communication line 5. Data from the computer 6 is received by the interface control part 1 in which the data is examined to determine to which character it belongs, the transmission control character or the display character. When it is a transmission control character, the data is processed in the interface control part 1. When it is a display character, the data is transferred to the display control part 2 in which the data is processed. The interface control part 1 sends the computer 6 data in given format comprised of the combination of transmission control data generated in the interface control part 1 and a display character supplied from the display control part 2 to the interface control part 1. In this manner, the interface control part 1 controls the data which it receives and transmits.
The display control part 2 controls the display of data on the screen of CRT 3, controls the data exchange between the interface control part 1 and the refresh memory 11, controls the interface with the keyboard 4, controls data editing, and controls traveler format.
This prior art character display device is operated in the following manner. When digits are supplied in sequence from the keyboard 4, a display will appear on the screen as shown in FIG. 2. In FIG. 2, reference numerals 21-1(a), 21-1(b), . . . , 21-m(n) represent display addresses on the screen, and reference numeral 22 represents a traveler. Assume the traveler 22 is present in the address 21-2(a). When the number of digits "123" is displayed on the screen by a data input device such as a keyboard, the traveler 22 advances one by one at each data input. Thus, at the end of the input, the traveler 22 is in the address 21-2(d). Assume the operator feeds "1234" to be displayed in the row beneath "123", and then "12345" to be displayed in the row beneath "1234", as shown in FIG. 2 wherein digit places differ by the individual numbers. A similar problem occurs with the display of a decimal point. In FIG. 3, the reference numerals 31-1(a), 31-1(b) . . . , 31-m(n) denote display addresses on the screen, and reference numeral 22 denotes traveler. Assume the traveler 22 is present in the address 31-1(a). When the operator generates an input data "12.3" for display on the screen by way of the keyboard, the traveler 22 advances one by one at each data input. At the end of the input, the traveler 22 is in the address 31-1(e). Further, assume the operator generates "123.45" and then "12.345" for display on the screen. As shown in FIG. 3, digit places and decimal places differ by the individual numbers. If digit places and decimal places are desired to be coordinated, the operator should determine the traveler position each time he generates an input digit. This has hampered the achievement of substantial man-machine interface capabilities of a character display device. Solutions to the prior art problems have long been awaited.